In the related art, an optical measurement using flow cytometry (flow cytometer) has been used for an analysis of biological microparticles such as a cell, a microorganism and a liposome. The flow cytometer is an apparatus that radiates light to microparticles passing through a flow path formed in a flow cell or a micro chip, and the like, detects fluorescence or scattered light emitted from the individual microparticles, and analyzes the detected result.
The flow cytometer includes a function of separating and collecting only microparticles having specific characteristics, and particularly, a microparticle apparatus targeting a cell as an object to be fractionated is referred to as a “cell sorter”. The cell sorter generally employs a droplet charging method that charges and separates droplets containing the microparticles as a fractionation method (refer to PTLs 1 to 3).
For example, in the flow cytometer described in PTL 1, a charging ring is disposed at a position (break-off-point) where droplets are separated from a carrier fluid and charges are selectively given to the droplets of the object to be fractionated. Further, a travelling direction of the charged droplets is changed by a droplet deflection plate disposed downstream from the charging ring, and the charged droplets are collected in predetermined containers or the like.
On the other hand, in the microparticle fractionating apparatus described in PTL 2, a microtube for introducing a sample liquid to an interior of a sheath liquid laminar flow is configured of a metal, and positive or negative charges is given to a sheath liquid and a sample liquid which pass through the interior of the flow path by applying a voltage to the microtube. In addition, in the microparticle fractionating apparatus described in PTL 3, a charging electrode is provided in a portion of the flow path provided in a microchip. Furthermore, in the microparticle fractionating apparatus described in PTLs 2 and 3, a ground electrode is disposed between an orifice and an electrode (droplet deflection plate) in order to eliminate influence of high potential of the electrode pair changing the travelling direction of the droplets.